1. Field of the Invention
This invention relates to air springs using a substantially tapered flexible air sleeve, and more particularly to an air spring capable of sufficiently reducing friction and effectively preventing the occurrence of wrinkles in a turned-up portion of the air sleeve when it is applied to a structure of changing a deflection angle between axis of piston and axis of end cap in expansion and contraction operation.
2. Related Art Statement
In a known diaphragm type air spring, there is a straight-type air sleeve 1 having uniform inner and outer diameters over its whole length is airtightly connected at its end portions to a piston 2 and an end cap 3, respectively, as shown in FIG. 4a.
In the air spring using such a straight-type air sleeve 1, however, the distance of elastic hysteresis loop in a direction of the minor axis becomes fairly long as shown in a load-displacement curve of FIG. 4b and hence the distance between intersections of hysteresis loop and load axis or a so-called friction is large. For instance, when the air spring is applied to an automotive vehicle, if vibrations having an amplitude of about .+-.10 mm are transmitted thereto, these vibrations cannot effectively be absorbed by the air spring, so that the ride comfortability of the vehicle is considerably damaged.
Recently, in order to sufficiently reduce the above friction and ensure the large stroke of piston 2 to end cap 3, there has been proposed an air spring with an air sleeve 4 having a substantially tapered form as sectionally shown in FIG. 5. It is airtightly connected at its small-diameter end portion 4a to the piston 2 and at its large-diameter end portion 4b to the end cap 3. And also, the gauge of the air sleeve 4 is uniformly thinned to about 2 mm for greater reduction of friction.
For instance, when each of the above air springs is mounted to an automotive vehicle at a posture shown in FIG. 4a, or when the air spring is used so as to align the axis of the piston 2 and the axis of the end cap 3 on a common line, the friction is reduced to improve the ride comfortability on the vehicle and also vibrations having a small amplitude as well as vibrations having a large amplitude are sufficiently effectively absorbed.
In these conventional air springs, particularly air spring using a thin an air sleeve, however, when it is applied so as to cross the axis of the piston 2 and the axis of the end cap 3 with each other at a deflection angle .delta. under a service load by fixing the piston 2 and the end cap 3 to an unsprung member 5 and a sprung member 6 in a vehicle wherein the unsprung member 5 and sprung member 6 gradually extend toward the side direction of the vehicle, for example, as shown in FIG. 6. There is still a problem that when the air spring is deformed in a direction of increasing the deflection angle or in the expansion direction under a load larger than the service load, plural wrinkles 7 are always produced in a turned-up portion of the air sleeve 4 as shown by a phantom line to lower the durability of the air sleeve 4.